Process for capturing metal ions

ABSTRACT

Cations of metals other than the alkali metals may be precipitated practically completely from their aqueous solutions at a pH of 4 or higher by N-acylamino acids whose acyl group is alkanoyl or alkenoyl having seven to 25 carbon atoms, the acylamino group being connected with the carboxyl group by divalent alkylene having one to five carbon atoms. The voluminous precipitates include even more of the metal ions originally present and settle faster in the presence of small amounts of polyhydric alcohols, polyethers, alkali metal silicates, or alkali metal borates. Water polluted with heavy metals can be made potable by this method.

States atet 1 1 lnazuka et a1.

[451 Aug. 28, 1973 1 1 PROCESS FOR CAPTURING METAL IONS [75] Inventors: Shinlchl lnazuka, Tokyo; Masahiro Takehara; Ryonosuke Yoshlda, both of Kanagaw a, all of Japan [30] Foreign Application Priority Data 3,437,451 4/1969 Every et a1 210/54 X 3,467,684 9/1969 75/108 X 3,491,086 1/1970 Harvey 210/53 X 3,518,171 6/1970 Merker et a1. 210/59 X 3,634,230 l/l972 Odom et a1 210/52 Primary Etaminer-Samih N. Zaharna Assistant Examiner-Thomas G. Wyse Attorney-Hans Berman [57] ABSTRACT Cations of metals other than the alkali metals may be precipitated practically completely from their aqueous solutions at a pH of 4 or higher by N-acylamino acids whose acyl group is alkanoyl or alkenoyl having seven to 25 carbon atoms, the acylamino group being connected with the carboxyl group by divalent alkylene having one to live carbon atoms. The voluminous precipitates include even more of the metal ions originally present and settle faster in the presence of small amounts of polyhydric alcohols, polyethers, alkali metal silicates, or alkali metal borates. Water polluted with heavy metals can be made potable by this method.

12 Claims, 1 Drawing Figure .1oo-l---------------e- Aug. 10, 1970 Japan 45/69916 [52] US. Cl 210/50, 210/53, 210/54, 75/108, 423/11 [51] Int. Cl C02b 1/26 [58] Field of Search 75/108; 210/42, 50-54, 210/59; 252/180 [56] References Cited UNITED STATES PATENTS 3,041,374 6/1962 Gregory 75/108 X 3,337,555 8/1967 Billman et al.... 75/108 X 3,412,180 11/1968 Corley 210/59 X 3,433,738 3/1969 Black et al 210/54 CAPTURE RATE OF CADMIUM ION 5O 3 4 5 6 (equivalents) ADDED DISODlUM ACYL-L-GLUTAMATE PATENTEBmza ms CAPTURE RATE OF CADMIUM ION 5O O i I I I I I 1 2 3 4 5 6 (equivalents) ADDED DISODIUM ACYL- L- GLUTAMATE PROCESS FOR CAPTURING METAL IONS The present invention relates to a novel process for capturing metal ions, and more particularly it relates to a process for capturing metal cations which comprises adding as a capturing agent N-higher aliphatic acyl amino acid or a water soluble salt thereof to an aqueous solution containing metal cations.

For capturing metal ions, particularly heavy metal ions contained at low concentration in water, there has been proposed a precipitation process in which metal ions are separated in the form of the insoluble inorganic metal salt. This process, however, is only applicable to specific metal ions which form the hardly soluble salt with a precipitant. Also, the formed inorganic metal salt exists in very fine particles or in a colloidal state, which makes the filtration very difficult. Particularly in the mixture of different metal ions, the fonnation of the respective insoluble precipitatesand their removal steps are complicated. Moreover, a large amount of precipitant remains still in the liquid phase from which the precipitate has been removed and so many difficult points are encountered from the point of view of drainage treatment. From these reasons, this process is not satisfactory economically and practically.

An another process proposedhitherto is a ion flotation in which a water soluble surfactant as a collector is added to an aqueous solution containing metal ions and then air is bubbled thereinto to form a froth, thereby hardly soluble materials rise to the surface in the froth and are thus removed. However the collectors employed hitherto have their limited collectivity so that metal ions can not be collected up tothe infinitesimal amount. And this process is not economically feasible.

Recently, the pollution of rivers by harmful metals which are remained in very small amount in industry drainage becomes a serious problem. This is mainly environment pollution based on heavy metals such as cadmium, lead, mercury, and the like, and a countermeasure for it is desired eagerly.

An object of the present invention is to provide a commercially easily feasible process for capturing metal ions by which the above harmful heavy metal ions and other various metal ions can be removed and recovered substantially completely from their aqueous solution.

It has now been found that when N-higher aliphatic acyl amino acid or a water soluble salt thereof is added to an aqueous solution containing metal ions, a hardly soluble metal salt of large size precipitates promptly and the salt may be simply and substantially completely separated from the solution by the application of a conventional procedure.

The present invention also provides a satisfacotry process for capturing metal ions which has the following outstanding features:

Firstly, this process is applicable to all cationizing metals with exception of alkali metals (the periodic table group I, subgroup A of elements). The processes known hitherto, i.e. the precipitation process by the formation of inorganic metal salts and the ion flotation are only applicable to a part of metals and is compli cated in the capturing step.

Secondly, the hardly soluble metal salt aggregates in large particles and precipitates or crystallizes out, and

' therefore the aftertreatments such as a filtration are easy.

Thirdly, the metal ions can be captured substantially completely, whatever the concentration of the metal ions is in the liquid. For example, when disodium N hydrogenated tallow oil fatty acid acyl glutamate is applied to cadmium ions as a capturing agent, a concentration of cadmium ions ranging from 20,000 ppm to 5 ppm in the original solution may be reduced to under 0.01 ppm at one stroke. This concentration corresponds to the allowed concentration of cadmium ions in drinking water as provided for by WHO international standard.

Fourthly, the amount of N-higher aliphatic acyl amino acid or its water soluble salt necessary to capture metal ionsmay be equivalent or slightly excess amount with: respect to the metal ion content. the addition of this amount of N-higher aliphatic acyl amino acid (or its water soluble salt) gives the best capturing effect. It is not necessary to'add excess amounts of the capturing agent. In some case, the addition of too much of the capturing: agent rather brings about the dissolution of the insoluble salts precipitated and decreases the capturing efiect'. Because the addition of excess capturing agent is not necessary, almost no N-higher aliphatic acylamino acid or its water soluble salt remains in the mother liquor and hence there isalmost no load of the biochemicaloxygen demand (BOD) and the chemical oxygen demand (COD). Alos, since this capturing agent of the present process is apt to be disintegrated by the action of microorganisms, the treatment is easy even when the agent is added in such excess amount that the load of BOD and COD exceeds the permissible amount. In case of the known capturing agents, for example hydrogen sulfide, it is necessary to add an excess amount of hydrogen sufide over the metal ions to be captured and hence a large amount of hydrogen sulfide remains in the aqueous solution from which metal ions have been'captured, and the treatment of drainage becomes difficult.

Fifthly, from the metal salt'separated, the metal may be readily recovered as its water soluble salt or its oxide, and N-higher aliphatic acyl amino acid may also be readilyrecovered and reused.

These features cannot be found in other similar surfactants such as sodium alkylbenzenesulfonate, sodium lauryl sulfate and fatty acid soap. As to sodium dodecyl benzene sulfonate and sodium lauryl sulfate, they show little or no capturing action toward metal ions, as apparant from Table 2 shown hereafter. Also, fatty acid soap is not suitable as the capturing agent because of its poor capturing power.

It has been further found that certain compounds are effective as capturing assistants or flocculent assistants for the capturing agent of N-higher aliphatic acyl amino acid or its water soluble salt. That is to say, the capturing effect of metal ions by N-higher aliphatic acyl amino acid or its water soluble salt is remarkably increased by employing as capturing assistant one or more members selected from the group consisting of organic compounds having two or more alcoholic hydroxyl groups in the molecule, organic compounds having more than two ether linkages in the molecule, alkali metal silicate and alkali metal borate. When a very small amount of at least one of the above four kinds of capturing assistants is added to an aqueous solution containing metal ions together with N-higher aliphatic acyl amino acid or its water soluble salt, the N-higher aliphatic acyl amino acid (or its water soluble salt shows further remarkable capturing action and the hardly soluble metal salt formed precipitates out more promptly. Owing to such advantage, the metal ions contained in industry drainage may be completely removed by application of the most easy natural sedimentation process. Also, by using these capturing assistants, the reaction of N-higher aliphatic acyl amino acid (or its water soluble salt) and metal ions may be smoothly conducted. More concretely speaking, to an aqueous solution containing one or more of metal ions belonging to the periodic table of the elements group I, subgroup B to group Vlll, are added N-higher aliphatic acyl amino acid (or its water soluble salt) in an amount of about 0.01 10, preferably 1.0 4.0 stoichiometric equivalents of the metal ions contained therein and one or more of the four kinds of capturing assistants in about 10 10 percent by weight, preferably 10* percent by weight of the N-higher aliphatic acyl amino acid (or its water soluble salt) added, whereby the increased capturing effect is obtained as well as higher sedimentation velocity of the formed precipitate as compared when N-higher aliphatic acyl amino acid (or its water soluble salt) alone is added. And metal ions may be further efficiently separated by using the conventional sedimentation equipments such as precipitation pool and thickener. Owing to attainment of the increased capturing effect, metal ions may also be separated by using an ion flotation equipment.

N-higher aliphatic acyl amino acid or its water soluble salt which may be the capturing agent in the present process is an amino acid derivative having acyl group being introduced into amino group of various amino. acids. The higher aliphatic acyl radical may be alkanoyl or alkenoyl derived from saturated or unsaturated fatty acid having eight to 26 carbon atoms, preferably 12 to 22 carbon stoms, for example, acyl radical of fatty acid consisting of single component (such as lauric acid, palmitic acid, stearic acid or oleic acid), the acyl radicals of the naturally originating mixed fatty acids (such v as coconut oil fatty acid, tallow oil fatty acid, hydrogenated tallow oil fatty acid) or the acyl radical of a synthetic fatty acid (inclusive of branched chain fatty acid too).

The amino acid components are acidic amino acids such as glutamic acid, aspartic acid, a-aminoadipic acid, a-aminopimeric acid, cysteic acid, homocysteic acid and 2-aminoeicosane dicarboxylic acid; diaminodicarboxylic acids such as a, a'-diaminocitric acid, a, a-diaminoglutaric acid and a,a'-diaminoadipic acid; neutral amino acids such as glycine, alanine, a-aminobutyric acid, valine, norvaline, leucine, isoleucine, norleucine, phenylalanine, tryptophane and proline; basic amino acids such as lysine, ornithine, arginine, histidine and isolysine; sulfur-containing amino acids such as methionine, cystein, cystine, homocystine, penicillamine, B-thiolleucine and ethionine; hydroxyamino acids such as threonine, serine, tyrosine, B-hydroxyleucine, homoserine and oxyproline'; N- methyl or N-ethyl derivatives of these B-amino acids; w-lower alkyl ester of acidic amino acids such as glutamic and aspartic acids; O-acyl or O-methyl derivatives of hydroxyamino acids; N, N-di-lower alkyl or N-acyl derivatives of basic amino acids such as lysine and ornithine. In addition to these a-amino acids, B-amino acids such as B-alanine and B-aminoisobutyric acid; m-amino acids such as 'y-aminovalerianic acid and w-aminocaproic acid, wherein the acylamino group is connected with the carboxyl group by a divalent alkylene group of five carbon atoms; and N- methyl, N-ethyl derivatives of these amino acids may be also employed. These amino acids or their derivatives may be optically active forms or racemic.

As the water soluble salts of N-higher aliphatic acyl amino acids, there may be employed alkali metal salts such as lithium, sodium and potassium salts, the ammonium salt, and salts with organic bases such as methylamine, triethylamine, diethylamine and ethanolamine.

Among these N-higher aliphatic acyl amino acids and their water soluble salts, especially N-higher aliphatic acyl derivatives of acidic amino acids such as glutamic and aspartic acids and their water soluble salts have two carboxylic groups and hence when they are employed as the capturing agent the capturing effect is obtained by the addition of a smaller amount of them and the formed precipitates are large particles having a good filterability. Also, the respective N-higher aliphatic acyl derivatives of phenylalanine, cystein, cystine and tryptophane are the preferred capturing agents. However, N-methyl-N-higher aliphatic acyl amino acid salts have somewhat weak capturing abilities.

Among the capturing assistants or the flocculant assistants which may be employed together with N-higher aliphatic acyl amino acids or their water soluble salts in the present invention are following: That is to say, examples of organic compounds having two or more alcoholic hydroxyl groups in the molecule include lower polyhydric alcohols such as ethylene glycol, propylene glycol, glycerin and sorbitol; monosaccharides such as glucose, galactose, dextrin, xylose; polysaccharides such as maltose, lactose, starch (inclusive of oxidized starch, enzyme-treated starch) and cellulose powder; hydroxyalkoxylated saccharides which may be prepared by reacting ethylene oxide and these saccharides; cyanoethylated starch; carboxyethylated starch; high molecular compounds such as polyvinyl alcohol, polypropylene alcohol. Examples of compounds having more than two ether linkages in the molecules include polyalkylene glycols such as polyethylene glycol, polypropylene glycol, nonionic surfactant containing polyoxyethylene group. Examples of alkali metal silicates include lithium silicate, sodium silicate and potassium silicate. And, examples of alkali metal borate include lithium borate, sodium borate and potassium borate. As to these silicates and borates, those of various composition may be employed.

These capturing assistants may be soluble in water or capable of emulsifying and dispersing uniformly in water. Among these compounds, especially polyethylene glycol having moelcular weight of 400 6,000, polyvinyl alcohol having molecular weight of 400 2,000, sodium metasilicate or sodium metaborate, when added singly or as admixture to an aqueous solution containing metal ions, promotes the aggregation and sedimentation velocity remarkably.

As to the order of the addition of the capturing assistant, it is desirable that N-higher aliphatic acyl amino acid (or its water soluble salt) is first added to an aqueous solution containing metal ions, thereby a hardly soluble metal salt is formed, and thereafter the capturing assistant is added thereto. Of course, the capturing assistant may be added in advance to an aqueous solution containing metal ions and then N-higher aliphatic acyl amino acid (or its water soluble salt) may be added. Otherwise both may be added simultaneously. Also, when the higher molecular compounds are em ployed as the capturing assistant, the higher the molecular weight is, the greater is the effect for promoting aggregation and sedimentation.

The amount of the capturing assistant to be added may be about 10 percent by weight of the amount added of N-higher aliphatic acyl amino acid (or its water soluble salt) for attainment of the desired sufficient effect. On the other hand, when the capturing assistant is added in exceedingly large amount, an appreciable capturing effect is not obtained and solubliza tion of the hardly soluble metal salt formed offen occurs. Also, a mixture of different capturing assistants gives a better result as compared to that of a-single'capturing assistant.

The metal ions which may be captured according to the present process are the periodic table group I,,subgroup B of elements such as copper and silver; group II of elements such as magnesium, calcium, strontium, barium, radium, zinc, cadmium and mercury; group III of elements such as aluminium, gallium, indium, thallium, scandium, yttrium, rare earth elements such as lanthanum and actinide elements (e.g-. uranium, actinium); group IV of elements such as germanium, tin, lead, hafnium, zirconium, and titanium; group V of elements such as antimony, bismuth, arsenic, vanadium, niobium and tantalum; group VI of elements such as chromium, molybdenum, tungsten, selenium, tellurium and polonium; group VII of elements such as manganese and technetium, and group VIIIof elements such as iron, cobalt, nickel, palladium and platinum. Also, metal ion may be organic metal or complex cation.

In accordance with'one embodimentof the present process, an N-higher aliphatic acyl amino acid or its water soluble salt is added directly or as a solution in water, suitable water-miscible organic solvent such as methanol or ethanol or their mixtures to an aqueous solution containing the metal ions as mentioned above, the amount added is about 0.01 to 10 equivalents, preferably 1.0 to 2.0 equivalents per equivalent of metal ions. If desired, the capturing assistant as specified already may be further added thereto in about 10 to 10 percent by weight of N-higher aliphatic acyl amino acid (or its water soluble salt), and thereby an insoluble or hardly soluble metal salt having a good filterability aggregates and precipitates immediately. The precipitates may be easily separated by the conventional solidliquid separation procedures such as filtration and decantation. It is desirable to add N-higher aliphatic amino acid (or its water soluble salt) to a solution containing metal ions at pH above 4. In case that an aqueous solution containing metal ions is above pH 8, N- higher aliphatic acyl amino acid, preferably Nhigher aliphatic acyl acidic amino acid is added and thereby metal ions may be effectively captured and the solution may be made neutral. Also, the temperature of treatment may be optionally selected but the room temperature is preferable. According to the present invention, the aggregation and sedimentation of the hardly soluble metal salt formed is completed in a short time. After treatment the residual metal ion concentrations in the mother solution or in the supernatant solution were measured by using an atomic adsorption photometer or a colorimeter and it becomes evident that almost no metal ions was detected and that the salts were filtered off or aggregated and precipitated substantially completely.

The precipitates separated are decomposed, for example, by treating with mineral acid and the metal ions may be recovered as the water soluble salt. Also, the precipitates may be burned to recover the metals as metal oxides.

The present invention is further illustrated by the following examples.

EXAMPLE 1 Nine aqueous solutions of cadmium sulfate containing 5' 10,000ppm ascadmium ion-were prepared, and 1.2, equivalent. of disodium N-hydrogenated tallow oil fatty acid acyl-L-glutamate was added as a 2.0 percent aqueous solution to the respective solutions. The stirring'was continuedat room-temperature and thereby a large amount of insoluble cadmium salt crystallized out. The crystals were filtered out with a filter paper (Toyo filter paper No.5A The residual cadmium ion concentrationsin the mother solution were measured by using an atomic adsorption photometer. The results were shown in Table 1.

TABLE 1 The Cd conc. in The Cd conc. The pH of the the original in the mother solution treated solution solution 10.000 ppm 0.100 ppm 6.40

EXAMPLE 2 With respect to twelve metal ions as shown in Table 2', aqueous solutions of 100 ppm concentration and aqueous solutions of 20 ppm concentration were prepared respectively. 1.2 Equivalent of the individual N- higher aliphatic acyl amino acid salt shown in Table 2 was added to each solution as the 2.0 percent aqueous solution, and the mixture was treated in a similar manner'as in Example 1. The results obtained were shown in Table 2. For the purpose of a comparison, the results obtained when the similar test was conducted with sodium dodecyl benzenesulfonate, sodium laurylsulfate, and fatty acid soap are also shown in the same table.

As is apparent from Table 2, N-higher aliphatic acyl amino acid salts have remarkable capturing activities to metal ions.

EXAMPLE 3 2.0 percent aqueous solutions of various N-higher aliphatic acyl amino acid salts as shown in Table 3 were prepared and the solutions were respectively added dropwise to aqueous solutions containing 100 ppm of Hg, A1 Sn, Pb, C0 Ni and U under the sameconditions as in Examples 1 and 2. The resultant slurry in every case was filtered out by the following two different methods.

i. treated with activated charcoal and then filtered out using a filter paper (Toyo filter paper No.5A).

ii. filtered out with a sand filter compacted with sands of various sizes and shapes.

The residual metal ion concentration in the respective filtrates was measured by using an atomic adsorption photometer. The results are shown in Table 3.

TABLE3 Metal ions Capturing agents The present invention:

5 m0000500m05000 2 7182 Q OQUWQAMIMOOOOI MMWW 0 0 0 0 0 Q00 O 0 0 0 0 0 0 5050 0 00050000 mmmamn nommemwmm m 20008 50005 0 5 00 memnwmmwmn snmmsmm 0 54 7500 l 050 25 memmwmwmmmmmmwmmww 5739-5069520001001 mm mmmmwmmmmmnmnwm 00 0 0 0 0 Q0 00 0 0 0 Q0 0 0 0 025 87055 059u 7 02 mmwmmmmmmmmmmmmmwm 0 00 0 0 0 0 0 0 0 0 0 0 0 0 Q0 0 50 0 2 552 ow-D 72 mmmowmmmmmmmommmmm Control:

587577 0 5 0 0 .& 22 352 ($2 0 W4351m 5505MB 5 05 253%2W 6520w Sodium lauryl sulfate.

Sodium dodecyl benzene sulfonate Fatty acid soap material.....

was added 1.5 equivalent of -coconut oil fatty acid ac ption photometer. the mother solution EXAMPLE 7 To a 90 percent methanol solution containin ppm of cupric chloride monosodium N yl-L-glutamate formed precipiurement of EXAMPLE 8 Two aqueous solutions of cadmium sulfate of 100 ppm and ppm with respect to cadmium ion concen- -hydrogenated tallow oil fatty lter paper the residual cadmium ion concentration in the filtrate was measured by using an 55 atomic adsorption photometer. The results are shown glycol and the ual cadmium ion concentration in the mother solution was measured with an atomic adsor The result was 0.007 ppm. Also was approximately neutral.

as 90 percent methanol solution. The tate was filtered off. The result of the meas the residual cupper ions in the mother solution by an atomic adsorption method was less than 0.01 ppm.

tration were prepared. To the solutions were added 1.2 equivalent of disodium N acid acyl-L-glutamate in the form of 2.0 percent aqu ous solution and polyethylene glycol having the molecular weight of 400 in the ration of 0.01 g per liter of the original solution. The stirring was continued at room temperature, whereupon a large amount of hardly soluble cadmium salt precipitated immediately. The sedimentation velocity of the cadmium salt formed was measured by the method described below. Also, after the precipitate was filtered off with a ti (Toyo filter paper No.5A

in Table 4.

For the purpose of comparison, a similar test was carried out in the absence of polyethylene result is also shown in the same table.

TABLE 4 ydrogenatcd tallow oil {None y -L-glutamate.

ethylene. Do. Glyc0l.

fatty acid 210 EXAMPLE 5 Various amounts of 2.0 percent aqueous solution of disodium N-hydrogenated tallow oil fatty acid acyl-L- queous solution 40 pm of cadmium p between -hydrogenated tallow EXAMPLE 6 To an aqueous solution of pH l 1 containing ppm of cadmium ions, was added a solution of 1.0 equivalent of N-stearoyl-DL-glutamic acid in ethanol. The

Capturing agent Disodlum N-h 1 Upper step: treated with activated charcoal.

2 Lower step: passed through a sand bed.

Nora-The concentration of metal ions in the original solution: 100 p.p.rn.

EXAMPLE 4 1.0 ml of 2 percent aqueous solution of disodium N- hydrogenated tallow oil fatty acid acyl-L-glutamate was acid salt has satisfactory capturing activity to complex ions.

added dropwise to an aqueous solution containing 100 ppm of hexaminecohalt (Ill) ions as a complex ion. The precipitated solid was filtered off and the residual complex ion concentration in the mother solution was measured with an atomic adsorption photometer. The result was 0.48 ppm. Thus, N-higher aliphatic acyl amino glutamate were added dropwise to an a of cadmium sulfate containing l00 p ions with stirring. The precipitated solid was filtered off and the amounts of residual cadmium ion in the filtrates were measured with an atomic adsorption photometer. The FIGURE shows the relationshi the amount added of disodium N oil fatty acid acyl-L-glutamate and the rate of cadmium ion captured. It will be seen from the FIGURE that this capturing agent has good capturing action to cadmium ions at wide ranges of the, amount added, and its capturing power is not affected even when it is added in excess amount of more than 6 equivalents.

formed insoluble precipitate was filtered off. The resid- Note: Th sedimentation velociy: a certain amount of the sample (slurry) was gathered in a test tube of 5.0 cm in diameter and 50 cm in height and the test tube was stoppered and then inverted times. The sedimentation velocity of the insoluble salt was then measured.

As is apparent from Table 4, the addition of polyethylene glycol brings effects to promote the sedimentation velocity and to increase the capturing effect.

EXAMPLE 9 There were prepared aqueous solutions of 100 ppm concentration respectively with respect to three kinds of metal ions shown in Table 5. In one case, to each solution was added 1.2 equivalent of each of several kinds 15 of N-higher aliphatic acyl amino acid salts shown in Table 5 as a 2.0 percent aqueous solution. In another case, polyethylene glycol having the molecular weight of 400 was further added thereto in the ratio of 0.02 g

per liter of the solution. in both cases, the stirring was continued at room temperature whereupon a large amount of the hardly soluble metal salt precipitated. The sedimentation velocities of the floc formed and the amounts of the residual metal ion concentration in the motor solution after filtration were measured as in Exfonate or fatty acid soap in place of Nhigher aliphatic acyl amino acid salt.

Note:

The value in the upper step of each item: no polyethylene glycol was added. The value in the lower step of each item polyethylene glycol was added.

EXAMPLE 10 To an aqueous solution of cupric sulfate, the concentration of which was 100 ppm, were added 1.2 equivalent of disodium N-hydrogenated tallow oil fatty acid acyl-L-glutamate as 2.0 percent aqueous solution and various kinds of flocculant assistants. The stirring was continued at room temperature, whereupon a large amount of the hardly soluble copper salt precipitated immediately. The sedimentation velocity of the salt precipitated and the residual copper ion concentration in the mother solution after the filtration were measured as in Example 8 to evaluate the capturing activities. The results were as shown in Table 6.

As is apparent from Table 6, four kinds of compounds, namely compounds having more than two hydroxyl radicals or ether linkages in the molecule, alkali metal salts of silicic acid and alkali metal salts of boric acid promote the aggregation and the velocity of the sedimentation.

Metal ion Cd (as CdSOl) Item to be measured Residual Residual Cd+ cone. Cu conc. Residual in the Sedimenin the Sedimen- Pb cone. Sedimenmother tation mother tation in the tation solution velocity solution velocity mother velocity Capturing agent (p.p.m.) (m./hr) (p.p.m (m./hr (p.p.m.) (rm/hr.) Disodium N-coconut oil fatty acid acyl-L-glutamate. 0. 020 0.80 0. 50 O. 70 (8)2 0. 007 2. 55 0. 10 2. 05 Potassium N-lauroyl-DL-omithine 0, 021 0. 60 0.26 0. 33 1). 32 1.28

0. 010 1. 70 0. 05 2. Sodium N-hydrogenated tallow oil fatty acid acyl- 0.004 1.30 0. 25 1.43 1.50 1.30 L-phenylalenmate. 0.002 4. 00 0. 02 4. 00 0. 7. 50 Sodium dodecyl benzene sulionate 99.1 0,0 92,8 0. 0 9s. 2 8.8

99. 0 0.0 93.5 0.0 99.0 Fatty acid soap materiel 78.5 0.1 40. 3 0. a 3. 8.;

TABLE 8 Residual Residual Cu con- Sedimen- Cu" con- Sedimencentratation centratation tion, velocity, Evalution, velocity, Evalu. occu an ass s an p.p.m. m. r. a on occu an ass s an p.p.m. m. r ation Fl 1 t i t t /h ti Fl l t i t t None 0.50 0.70 Gelatine 0.50 0.7 X Calcium oxide 0.60 0. 45 X 0. 40 1. 30 A Calcium hydroxide 1. 30 0. 30 X 0.50 0. 70 X Sodium carbonate 1. 30 0. 20 X 0. 76 0.50 X Sodium hydroxide 1. 00 0.20 X 1. 00 0. X s e 2'92 8218 3'13 H8 $3 erroussu a e Ammonium bicarbonate 0. 0. X Cellulose powder; 0. 20 1. O Thiourea 0. 50 0. 50 X Ethylene glycol 0. l0 1. 50 O Urea 0.50 0. 70 X Glycerin 0.30 1. 60 A Ammonium fox-mate 0. 50 0.50 X Polyethylene glycol (MW. 400).... 0.10 2. 06 0 Sodium bicarbonate 3.20 0.35 X Polye thylenc glycol (M.W. 1500)... 0.05 3. 86 O Disodium phosphate 1.20 0.50 X Polyethylene glycol (MW. 4000)... 0. 02 4.00 Sodium meteborate.. 0. 10 1. 60 O Polyethylene glycol (M.W. 6000)... 0.30 2. 00 Sodium metasilicate 0. 05 1. O Xylose 0. 20 1. 80 0 Sodium orthosilicate 8. E0] 1). 273 1Egly {1521 8. 2g 8. 70 X en 0 to 70 X Polyacryl (p y ro y 0. 50 0x70 X Cement dust U 50 0, 70 X Sodium polyacrylate 0. 70 0. 40 X Maleic acid resin 0. 0. 70 X Sodium polyglutamate. 0.90 0.30 X Water soluble urea resin H 0. 50 0. 70 X Polyvinyl acetate 0. 60 0. 75 X Cationic polyurea 0. 50 0. 70 X Polyvinyl pyridine 0.50 0. 70 X Polyaminotriazole 0. 60 0. 70 X Polyvinyl pyrrolid -ne 0. 50 0. 70 X Polyoxyethylene dodecyl other... 0. 40 1.00 A

Nora-Evaluation criteria:

X=does not promote the aggregation and the velocity of the sedimentation. A=promotes appreciably the aggregation and the velocity of the sedimentation. O=promotes remarkably the aggregation and the velocity of the sedimentation.

To 1 liter each of an aqueous solution containing 100 ppm of ferric ion, was added 1.2 equivalent of dipotassium N-stearoyl-DL-glutamate as 2.0 percent aqueous 14 respective capturing assistants was 5.0 mg. It will be seen from Table 8 that the use of the mixture of capturing assistants gives better result as compared with the use of single capturing assistant.

solution and 0.01 50 mg of polyethylene glycol having What we claim is: molechlat Weight of 9 to 6,000 or -Q 50 mg of l. A method of removing cations ofa metal of Group P y y q p having molecular Weight of 500 lb or of Groups ll to VIII of the Periodic Table of the 2,000.The stirring was continued at room temperature. Ehhems f their solution in an aqueous medium After settling, the sdeimentation velocity of the floc which comprises; formed and the residual ferric ion concentration in the dissolving in said medium an amount f an mother solution after filtration were measured as in Exacylamino acid or f a water Soluble n f Said ample 8 to evaluate the ability of the flocchlaht acid sufficient for substantially completely precipitants to promote the aggregation and the sedimentation tatihg said cations, velocity. The results are summarized in Table 7. L the PH f said medium being at least 4 TABLE 7 2. the acyl radical of said N-acylamino acid being F] l l Amounts added (my alkanoyl or alkenoyl having 7 to 25 carbon atom,

wei gli t 0.01 0.05 0.10 0.50 1.0 5.0 10.0 50.0 h acylammo grollp of sad N acylammo i being connected with a carboxyl group of said 28g 2 Q g g 8 $2 52 N-acylamino acid by divalent alkylene having 9 A A A one to five carbon atoms; and Polyvinyl '500 A A A A O O O X b. separating the precipitated cations from said mealcoh0l 1,400 O 0 O O O O A A 2,0000QOAAAAA 2. A method as set forth in claim 1, wherein said Note) Evaluation criteria amount is 0.0] to 10 stoichiometric equivalents of said x The Fe concentration in the mother solution 3.5 catimm pm, the sedimentation velocity 0.7 m/hr 3. A method as set forth in claim 1, wherein said A 3 The concentration PP The Sethamount is 1.0 to 4.0 stoichiometric equivalents of said mentation velocity 0.7 1.5 m/hr cations.

O 1 h t cohcehtfatioh less than PP The 30 4. A method as set forth in claim 3, wherein said al- Sedhhehtatloh veloclty g than kanoyl or alkenoyl has 11 to 21 carbon atoms.

From these experimental results, it was recognized 5 A method as Set f rth i l i 1, h i an that the higher is the molecular Weight ofa g "1 amount of at least one capturing assistant effective for hh Series of flocculaht asslstahtsv the greatet the enhancing the settling velocity of the precipitated cath y to P t the aggre g atlh and the Sedimenta- 3 5 ions in said medium and for reducing the concentration ttoh Velocity, Whlle the addltloh of excess ahlOUhtS of of residual cations in said medium after said precipitatthem dld not show pp hh capturing effect, ing is dispersed in said medium, said capturing assistant and the excess assistants solublllzed the metal salt being an organic compound having two or more 1 formedholic hydroxyl groups, an organic compound having a EXAMPLE 12 40 polyoxyethylene radical including more than two ether To 1 m each f an aqueous solution containing 100 linkages, an alkali metal silicate, or an alkali metal boppm of ferric ions, were added 1.2 equivalent of soratedium N-hydrogenated tallow oil fatty acid acyl-DL- A method as Set forth In Claim wherein the methionine as 2.0 percent aqueous solution and capturamount of 581d p ring a sistant is between 10* and ing assistants shown in Table 8 singly or in admixture 0 per nt Of the weight of said N-acylamino acid. of two components. The sedimentation velocity of the 7- A method as set forth in claim 6, wherein the formed floc and the residual ferric ion concentration in amount of said Capturing assistant is between l0 and the mother solution after filtration were measured and 10 percent of said weight. the results are summarized in Table 8. 8. A method as set forth in claim 6, wherein said cap- TABLE 8 Poly- Polyethylene vinyl Sodium Polyglycol alcohol methasll- Soluble acrylic (500) icate Starch amide (B) (A) (A) (A) Sodium methasihcate Soluble starch 0.50

Polyacrylic amide 0.65 4.05 0.45

Note) turing assistant is a polyhydric alcohol.

A. Each column shows the residual ferric ion concentration (unit ppm) in the mother solution resulted by using a filter paper (Toyo filter paper No.5A).

B. Each column shows the sedimentation velocity (unit m/hr) of the floc.

The residual ferric ion concentration in the mother solution when no capturing assistant was added was 4.05 ppm. The sedimentation velocity of the floc formed when no capturing assistant was added was 0.45 m/hr. The amount added of the of said medium is lower than 8 after said dissolving.

UNITED STATES PATENT OFFICE QERTIFICATE OF CORRECTION Patent No. 3,755,158 w Dated August 28, 1973 It is certified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

In' the heading, line $97, after Aug 10, 1970 Japan 45/69916" insert ooeamooooom Signed and sealed this 20th day of November 1973.

(SEAL) Attes't:

EDWARD M.FLETCH ER,JR. RENE D. TEGIMEYER Attesting Officer Acting Commissioner of Patents FORM PC4050 uscoMM-Dc 60376-P69 k .5. GOYERNMENT PRINTING OFFICE 1 I969 0-366-33.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,755,158 Dated August 28, 1973 InVentor(S) SHINICHI INAZUKA ET AL It is certified thaterror appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the heading, line after "Aug. 10, 1970 Japan 45/69916" insert Oct. 26,1970 Japan 45/94078 Signed and sealed this 20th dsy of November 1973,

(SEAL) Attest:

EDWARD M.ELET0EEE,JR. RENE D. 'TEGTMEYER Attesting Officer Acting Qommissioner of Patents FORM PO-1050 (-1 0-69) f u.s. sgyznumzm' PRINTING OFFICE: 1909 0-366-334. 

2. A method as set forth in claim 1, wherein said amount is 0.01 to 10 stoichiometric equivalents of said cations.
 2. the acyl radical of said N-acylamino acid being alkanoyl or alkenoyl having 7 to 25 carbon atom,
 3. the acylamino group of said N-acylamino acid being connected with a carboxyl group of said N-acylamino acid by divalent alkylene having one to five carbon atoms; and b. separating the precipitated cations from said medium.
 3. A method as set forth in claim 1, wherein said amount is 1.0 to 4.0 stoichiometric equivalents of said cations.
 4. A method as set forth in claim 3, wherein said alkanoyl or alkenoyl has 11 to 21 carbon atoms.
 5. A method as set forth in claim 1, wherein an amount of at least one capturing assistant effective for enhancing the settling velocity of the precipitated cations in said medium and for reducing the concentration of residual cations in said medium after said precipitating is dispersed in said medium, said capturing assistant being an organic compound having two or more alcoholic hydroxyl groups, an organic compound having a polyoxyethylene radical including more than two ether linkages, an alkali metal silicate, or an alkali metal borate.
 6. A method as set forth in claim 5, wherein the amount of said capturing assistant is between 10 7 and 10 percent of the weight of said N-acylamino acid.
 7. A method as set forth in claim 6, wherein the amount of said capturing assistant is between 10 5 and 10 1 percent of said weight.
 8. A method as set forth in claim 6, wherein said capturing assistant is a polyhydric alcohol.
 9. A method as set forth in claim 6, wherein said capturing assistant is a saccharide.
 10. A method as set forth in claim 6, wherein said capturing assistant is a polyalkylene glycol.
 11. A method as set forth in claim 6, wherein said capturing assistant is an alkali metal silicate or alkali metal borate.
 12. A method as set forth in claim 1, wherein the pH of said medium is lower than 8 after said dissolving. 